1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, facsimile machine, printer, plotter or multifunction machine, and more particularly, to a developing device for developing an electrostatic latent image on an image carrier by supplying a one-component developer to the image carrier, and to a process cartridge provided with the developing device.
2. Description of the Related Art
Conventional developing devices for developing an electrostatic latent image on an image carrier by supplying a one-component developer to the image carrier include the following known technologies.
(1) A developing device (for instance, as disclosed in Japanese Patent No. 2987254) comprising a conductive member (recovery blade) brought into contact with a developer carrier (developing roller) at a position on a downstream side from the position of a part to be developed, with respect to the rotation direction of the developer carrier; and a voltage application means for applying, to the conductive member, a voltage of the same polarity as that of the developer carrier and equal to or above that of the developer carrier.
(2) A developing device (for instance, as disclosed in Japanese Patent Application Laid-open No. 2001-117366) in which developer is electrically supplied and recovered by applying an AC voltage to a developer carrier (developing roller) and applying a DC voltage to a developer supply and recovery member (reset roller).
(3) A developing device (for instance, as disclosed in Japanese Patent No. 3283143) in which, after development, a conductive mesh member, formed by weaving conductive fibers into a mesh, and to which a voltage has been applied, is made to abut a toner layer surface of a developing roller, the mesh member being swingable relative to the developing roller.
In the technology (1), however, good images can be obtained, without printing history becoming apparent, by controlling the electrostatic flocculation state of residual developer after development, to cancel thereby the difference in charge between printed portions and non-printed portions. When the developer becomes harder to charge owing to impaired durability or the like, it is no longer possible to wholly cancel the charge difference between printed and non-printed portions, whereupon printing history may become visible on the image.
Further, in the technology (2), good images can be obtained, without printing history becoming apparent, over long periods of time, by recovering residual developer, after development, by way only of electric forces arising from bias applied between the developer supply and recovery member and the developer carrier. When the amount of charge of the developer drops on account of, for instance, impaired durability or the like, recovery by electric forces may become insufficient, whereupon printing history may become visible on the image.
Furthermore, in the technology (3), good images can be obtained, without printing history becoming apparent, by leveling the developer, after development, using a swingable conductive mesh. However, developer turnover on the developer carrier is difficult by leveling alone, and developer deteriorates more readily on the developer carrier, which may preclude achieving good images over long periods of time.